Fix android-code-coverage infra failure

android-code-coverage keeps failing https://ci.chromium.org/p/chromium/builders/luci.chromium.ci/android-code-coverage
Looks like it is searching for 8 cores, which should be 32 cores, e.g.:
https://chromium-swarm.appspot.com/task?id=453ef7394666fa10&o=true&w=true


Bug: 967011,961808
Change-Id: Ib1b958e0e27c29868cad080786a9aa83767c2773
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1644878Reviewed-by: Michael Moss <mmoss@chromium.org>
Reviewed-by: John Budorick <jbudorick@chromium.org>
Commit-Queue: John Budorick <jbudorick@chromium.org>
Cr-Commit-Position: refs/heads/master@{#666301}

infra/config/cr-buildbucket.cfg

@@ -1093,6 +1093,7 @@ buckets {
       mixins: "code-coverage"
       mixins: "linux"
       dimensions: "os:Ubuntu-14.04"
+      dimensions: "cores:32"
     }
 
     builders {